The invention relates to a cross-cutter for cutting web material, in particular corrugated cardboard, according to the preamble of claim 1.
Cross-cutters for corrugated cardboard production apparatus normally include pairs of knife shafts in which each shaft holds at least one knife with a continuously extending cutting edge which has a uniform distance from the shaft axis. The knife blade either extends in parallel to the shaft axis or is arranged helically. The helical arrangement has the advantage that during the cutting operation always only a short portion of the cutting edges are in engagement with each other at a single instant, whereby the loading on the knives, the knife retainer and the shafts is maintained low. The cutting edges of the knives describe circles which intersect slightly. The cutting edge of the one knife lies in the leading region of the knife blade and the other in the trailing region thereof. The radius of revolution of the cutting edge in the trailing region is selected to be slightly greater than the radius of the other cutting knife, so that only a single contact of the cutting edges occurs during one revolution, with the cutting edges moving apart relatively quickly after that contact.
The knife of at least one shaft is adjustably secured at a number of points. If a contact of the knife edges is no longer ensured due to wear, at least one knife requires adjustment. This job requires interruption of production and very much time. With tough material or from a certain grammage of the corrugated cardboard on or also with moist or coated corrugated cardboard, a not insignificant bias between the knives must be set to attain an unobjectionable cut. A greater bias involves high cutting forces. High cutting forces in turn necessitate adjustment of the knives at relatively short intervals, which causes undesired interruptions of production. High cutting forces also cause rapid wear of the knives. Since heavy materials to be cut do not occur very often, it would be more favourable in view of the service life of the knives to reduce the once adjusted high bias. Since, however, the usual adjustment of the knives is a time-consuming and complicated job, a relatively high knife bias is used in practice even in connection with light qualities. This means great knife wear and low knife service life, which are not so much due to the material than to the high bias.
Hence, the object of the invention is to provide a cross-cutter for cutting web material, in particular corrugated cardboard, in which the service life of the knives is prolonged.